1. Field of the Invention
The invention is a stabilizer for polymers of chlorine-containing olefins, a process for preparation of the stabilizer and polymers containing the stabilizer.
The stabilizer of the invention is useful for stabilizing PVC and PVC copolymers, particularly suspension, bulk and emulsion PVC.
2. Statement of Related Art
There is a trend to replace the heavy metal stabilizers used in rigid PVC products, such as lead and cadmium compounds, by stabilizers based on calcium and zinc. This change has been successful in certain fields. For example, PVC bottles for drinking water have been produced without heavy metal stabilizers for reasons of odor.
The production of calendered films based on Ca/Zn stabilizers does not present any problems, provided the films are opaque. However, the production of transparent or glass-clear films without heavy metal stabilizers is difficult. Relatively large quantities of epoxides, particularly epoxidized soybean oil, are required to stabilize the films. However, since these co-stabilizers have a plasticizing effect, they cannot be used in the manufacture of PVC pressure pipes. Nevertheless, even pressure pipes can be produced without difficulty using Ca/Zn stabilizers, cf. DE-OS 29 41 596. In cases such as these, however, the problem of adequate stabilization is solved by coloring the pipes dark grey or dark brown so that a good early color is not a key factor.
By contrast, rigid PVC is required to have an extremely good early color in the shaped article industry. Shaped article manufacture differs from pipe manufacture in that the shaped article cross-sections can be extremely complex and are often made with extremely thin walls. In addition, shaped articles generally require a good finish which frequently necessitates the addition of various modifiers which increase the viscosity of the PVC melt and complicate material flow. In this case, the known Ca/Zn stabilizers and added epoxides are not sufficient for effective stabilization, nor are additions of co-stabilizers, such as polyols or sodium aluminium silicates. Although polyols, such as pentaerythritol, improve the early color, they tend to sublime and cause plating in the calibrating units of the production lines, adversely affecting the surface quality of the shaped articles. Even the combined use of short-chain pentaerythritol esters (pentaerythritol mono-, di- and triacetates) and free polyols, has not produced a solution to this problem.
Although stabilization of chlorine-containing olefin polymers with commercial 1,3-diketones, for example benzoyl stearoyl methane, produces a light early color, this light early color is not retained in the course of processing for prolonged periods. The same disadvantages attend the stabilizing systems disclosed in DE-PS 27 16 389 which contain acetyl acetonates of calcium and/or magnesium in addition to calcium silicates or aluminates, mercaptans or mercaptides and calcium salts of monocarboxylic acids.
The present invention is a stabilizer for polymers based on chlorine-containing olefins which provides the polymers with the following advantageous properties:
1. freedom from heavy metals, PA0 2. stable or persistent early color, PA0 3. no discoloration at relatively high temperatures for the period of time required for the production of shaped articles, PA0 4. resistance to environmentaI factors, particularly where the shaped articles are used outdoors (UV stability), PA0 5. problem-free processibility of the stabilized polymers attributable to the absence of deposits on mold walls. PA0 (a) Ca complexes of 1,3-diketones of the formula EQU [R.sup.1 CO--CH.dbd.C(R.sup.2)--O--].sub.x Ca(OH).sub.y PA0 in which R.sup.1 and R.sup.2 can be the same or different and represent radicals selected from the group consisting of C.sub.1 -C.sub.4 alkyl, phenyl, phenyl substituted in the p-position; x has a value of 1 to 2 and y has a value of 1 to 0 with the proviso that x+y=2, PA0 (b) hydrocarbon wax and PA0 (c) at least one of full esters of saturated, straight-chain C.sub.12 -C.sub.34 monocarboxylic acids with polyols containing at least 2 carbon atoms and at least 2 hydroxy groups and partial esters of saturated, straight-chain C.sub.12 -C.sub.34 monocarboxylic acids with polyols containing at least 2 carbon atoms and polyols containing at least 2 hydroxy groups which, as a number average, contain at least one free hydroxyl group and, optionally, PA0 (d) zinc salts of saturated, straight-chain C.sub.8 -C.sub.22 monocarboxylic acids.